With rapid popularity of LED lamps, market sales volumes are increasing and the costs are decreasing. This promises a bright future for promotion of display screens with higher contrast and high definition. A conventional LED lamp typically consists of a plastic casing provided with a reflective cup, a package PCB disposed on the back of the plastic casing, where the reflective cup is provided with an LED chip electrically connected to the PCB and a light-guiding packaging adhesive.
To improve the contrast, a traditional LED lamp typically adopts the following solutions:
1. White casing with screen-printed black surface—a black coating 3 is screen-printed on the top surface of a white plastic casing 2, and a chroma contrast is formed between the surface of a white reflective cup 5 and a black coating 3 on the top surface thereof to enhance the contrast displayed by the product; where the reflective cup 5 is provided with an LED chip 1 and a light-guiding packaging adhesive 4, as shown in FIG. 1.
Disadvantage: Since the surroundings of the LED chip 1 and the inner surface of the reflective cup 5 are all white, the surfaces of the white plastics will reflect ambient light so that the contrast displayed by the product is reduced.
2. All-black casing—Black plastic replaces the original white plastic for injection molding of a casing, so that the surfaces of the casing 6 and the reflective cup 5 are black to enhance the contrast displayed by the product, as shown in FIG. 2.
Disadvantage: Since the surface of the reflective cup 5 inside the LED chip 1 is also black, light emitted by the LED chip cannot be better reflected from the surface of the black reflective cup, and luminance of the light emitted by the LED chip is greatly reduced. To solve the problem of the luminance, some manufacturers improve the luminance of the LED lamp by improving the LED current. This, however, goes against an energy-saving concept of the LED lamp, and also increases heat discharge of the product, and affects life of the LED lamp.
3. Outer-black and inner-white casing—Blank plastic is used for injection molding of the casing 6, and a reflective cup's lining 7 made by injection molding using white plastic is used. This makes a uniformly black appearance for the reflective cup from viewpoints of the outer and top portion of the reflective cup's lining. However, the surface of the reflective cup's lining 7 is white. This effectively enhances the contrast but does not reduce luminance of the light emitted by the LED chip, as shown in FIG. 3.
Disadvantage: Ambient light will be reflected from the surface of the reflective cup so that the contrast is reduced. In addition, since a three-layer composition structure is used, the water-proof effect is hard to achieve. Generally, manufacturers only use this structure for products having a lower water-proof requirement, and therefore adaptability is poor.
In view of the above, how to design a water-proof LED lamp with high contrast, low power-consumption and high adaptability is a technical issue to be addressed in the industry.